A lot of research done within the past decade has shown the remarkable role the endocannabinoid system has in the development of obesity. The age-old of paradigm of “weeds gives people the munchies” has lead to the belief that cannabis causes weight-gain. While everyone is different, a study from 2011 found that cannabis consumers were less likely to be overweight, one of the first indications that cannabis’ role in bodyweight is more complex than it seems.

This latest study from the University of Calgary and the Canadian Center for Addiction and Mental Health has proven that a relationship truly exists between body mass, cannabis consumption and the different microorganisms that live in your gut. They fed mice either a lean or high-fat diet, and injected them daily with either THC (roughly equivalent to a smoking a couple big joints) or placebo for six weeks. Mice fed the lean diet (13 % of calories from fat) didn’t gain weight whether they were injected with THC or not. Mice fed the high-fat diet (45 % of calories derived from fat) gained up to four grams, a hefty 20 % increase in body-weight. Mice on the high-fat diet that took THC every day didn’t gain any weight on average by the end of the trial.

The scientists also monitored changes in their intestinal flora, a.k.a. the symbiotic, beneficial microorganisms living in their intestines that play important roles in digestion, immunity and obesity. While the intestines of obese mice have a high ratio of Firmicutes relative to Bacteroides microbes, this latest study has found that daily THC administration kept the ratio under control in mice fed the high-fat diet, in addition to preventing weight gain. Interestingly THC increased levels of another microbe, Akkermansia muciniphila, in mice fed the high-fat diet, but not in those mice on the lean diet, highlighting the complexity of factors at play.

The study theorizes that THC may be interacting with the intestinal microbes in a way that prevents weight gain. Obese individuals have higher endocannabinoid tone in their intestines and adipose tissue, meaning higher levels of endocannabinoids, cannabinoid receptors, and their degrading enzymes. Cells in certain tissues in the body produce endocannabinoids like anandamide (AEA) and 2-arachidonoylglycerol (2-AG), which go on to activate cannabinoid receptors (CB1 and CB2) which are involved in regulate appetite, body temperature, pain-sensation, etc.

Increased levels of endocannabinoids in the gut of obese individuals indicated to researchers that a cannabinoid receptor antagonist, with opposing effects to an agonist, could reverse the effects of obesity. Trials for the drug rimbonant, a CB1 receptor antagonist, were initially successful in causing weight loss, but depriving the body of natural cannabinoid receptor activation had negative psychiatric effects including depression and suicide. Rimbonant was never approved by the FDA, and was only on sale in Europe for three years before being withdrawn.

THC on the other hand, is a partial agonist of both cannabinoid receptors: CB1 and CB2. Its unique effects on the body cannot be equated to full agonists like the powerful and dangerous ingredients in synthetic cannabis which can cause psychiatric events, seizures, coma, organ failure, etc. The researchers in Calgary believe this partial agonist activity of THC has some role in modulating gut flora and gut permeability. Their results are certainly promising, but much lies to be uncovered about the intricate relationship between the endocannabinoid system, the body’s microbiome and how cannabis may one day treat or prevent obesity and diabetes.